The temperature history in the casting obtained from cooling curves can be used to determine some information related to latent heat release during alloy solidification. This work presents a procedure for the evaluation of latent heat of primary and eutectic solidification of grey cast iron from cooling curves based upon the Newtonian cooling principle. The thermal data obtained from quik-cups are processed with the Mathcad code in order to obtain the cooling curve, its first and second derivatives and the first derivative of the fictitious neutral body generated according to the principles of Newtonian cooling assumption. The cooling curves of seven different alloys of hypoeutectic, eutectic and hypereutectic compositions were investigated with special emphasis oil the amounts of latent heat released during primary and eutectic solidification. The values obtained are consistent with the statement that the latent heat of eutectic solidification should increase as the composition of the cast iron comes closer to the eutectic point, but the methodology is found to be unreliable for the estimation of latent heat of primary solidification.